Image scanning apparatuses such as image scanners, copiers, printers and multi function peripherals (MFPs) are widely used in our daily lives or offices for scanning images of objects such as paper sheets. As known, the image scanning apparatus usually has an automatic document feeder for automatically and continuously feeding many paper sheets one by one. During operation of the automatic document feeder, the paper sheet is readily jammed, especially in the vicinity of the ejecting roller assembly.
Referring to FIG. 1, a schematic cross-sectional view of a conventional automatic document feeder is illustrated. The automatic document feeder 200 principally includes a paper input tray 202, a paper ejecting tray 204, a pick-up roller assembly 210, a transfer roller assembly 220, an inner roller assembly 230, an ejecting roller assembly 240, a first transfer path 250 and a second transfer path 260. The ejecting roller assembly 240 includes a driving roller 241 and a follower roller 242. The driving roller 241 and the follower roller 242 are fixed within the automatic document feeder 200 and in contact with each other to provide a specified nip force therebetween.
FIG. 2A is a schematic cross-sectional view illustrating that the paper sheet is transported out of the automatic document feeder. FIG. 2B is a schematic cross-sectional view illustrating that the paper sheet is transported into the automatic document feeder.
Hereinafter, the procedure of performing a single-side scanning operation by the automatic document feeder 200 will be illustrated with reference to FIG. 2A. First of all, the paper sheet 206 to be scanned is placed in the sheet input tray 202. The pick-up roller assembly 210 transports the paper sheet 206 into the first transfer path 250 (as indicated in FIG. 1). The paper sheet 206 is successively transported by the transfer roller assembly 220, the inner roller assembly 230 and the ejecting roller assembly 240. When the paper sheet 206 is transported across a scan region (not shown) in the first transfer path 250, a first side of the paper sheet 206 is scanned by a scanning module (not shown) under the scan region. Next, the driving roller 241 of the ejecting roller assembly 240 is rotated in an anti-clockwise direction to have the paper sheet 206 eject to the paper ejecting tray 204.
Hereinafter, the procedure of performing a duplex scanning operation by the automatic document feeder 200 will be illustrated with reference to FIG. 2B. After the first side of the paper sheet 206 is scanned by using the above produce and a majority of the paper sheet 206 is ejected to the paper ejecting tray 204, the driving roller 241 of the ejecting roller assembly 240 is reversely rotated in the clockwise direction, so that the paper sheet is transported into the second transfer path 260 (as indicated in FIG. 1). Next, the paper sheet 206 is successively transported by the transfer roller assembly 220, the inner roller assembly 230 and the ejecting roller assembly 240. When the paper sheet 206 is transported across the scan region, a second side of the paper sheet 206 is scanned by the scanning module. Next, the driving roller 241 of the ejecting roller assembly 240 is rotated in the anti-clockwise direction to have the paper sheet 206 eject to the paper ejecting tray 204.
Generally, the driving roller 241 and the follower roller 242 need to be in contact with each other so as to provide sufficient nip force for transmitting the paper sheet 206 into or out from the inner portion of the automatic document feeder 200. In a case that the nip force is too large, the paper sheet fails to be smoothly transferred across the region between the driving roller 241 and the follower roller 242, and thus the paper sheet is readily jammed. For preventing the paper sheet 206 from getting jammed between the driving roller 241 and the follower roller 242, the driving roller 241 and the follower roller 242 needs to be in loose contact with each other. Under this circumstance, the nip force may be insufficient for transmitting the paper sheet 206 into or out from the inner portion of the automatic document feeder 200. Moreover, since the driving roller 241 and the follower roller 242 of the ejecting roller assembly 240 are fixed within the automatic document feeder 200, it is difficult to adjust the nip force as required.
Therefore, there is a need of providing an ejecting roller assembly for used in an automatic document feeder to effectively prevent the paper sheet from getting jammed.